1. Field of the Invention
The invention relates to a direct current (DC) brushless motor, more particularly to a reluctance motor system.
2. Description of the Related Art
Referring to FIG. 1 and FIG. 2, two schematic diagrams respectively illustrate a front view and a side view of a conventional reluctance motor 1. The conventional reluctance motor 1 includes a stator 11 and a rotor 12 surrounded by the stator 11. The stator 11 includes eight salient poles A, A′, B, B′, C, C′, D and D′, and four phase winding sets wound around the eight salient poles. Each of the phase winding sets includes a first winding L1 and a second winding L2 that are connected in series, and that are respectively wound around two of the salient poles of the stator 11 that are diametrically opposite to each other. For example, the first winding L1 and the second winding L2 of one of the phase winding sets are respectively wound around the salient poles A and A′, the first winding L1 and the second winding L2 of another one of the phase winding sets are respectively wound around the salient poles B and B′, and so forth. The rotor 12 includes six projecting poles a, a′, b, b′, c and c′.
Referring to FIG. 3, a conventional driving circuit 2 for a reluctance motor is illustrated. The driving circuit 2 is to be coupled electrically to a direct current (DC) power source Vdc, and includes four switching members 21-24 that are connected in parallel with the DC power source Vdc. Each of the switching members 21-24 corresponds to a respective one of the four phase winding sets connected to the stator 11, and includes a first switch Qu coupled electrically to a first end of the respective phase winding set, a second switch Qn coupled electrically to a second end of the respective phase winding set opposite to the first end thereof, a first flyback diode D1 with a cathode coupled electrically to the first end of the respective phase winding set and with an anode to be coupled electrically to a negative terminal of the DC power source, and a second flyback diode D2 with a cathode to be coupled electrically to a positive terminal of the DC power source and with an anode coupled electrically to the second end of the respective phase winding set.
The driving circuit 2 is used to excite the reluctance motor 1 in a split-phase manner by exciting the four phase winding sets in sequence, that is, the driving circuit 2 controls one of the switching members in a fundamental cycle. For example, referring to FIG. 4, when the first switch Qu and the second switch Qn of the switching member 21 are conducting, the first winding L1 and the second winding L2 of a corresponding one of the phase winding sets is configured to form a current loop with the DC power source Vdc, such that a magnetic field is generated at each of the salient poles A and A′ around which the first and second windings L1 and L2 of the corresponding one of the phase winding sets are wound, so as to attract the projecting poles a and a′ of the rotor 12 to move toward the salient poles A and A′ of the stator 11, as best shown in FIG. 1. Subsequently, when the first switch Qu and the second switch Qn of the switching member 21 are not conducting, and when the first switch Qu and the second switch Qn of the switching member 22 are conducting, the first winding L1 and the second winding L2 of another corresponding one of the phase winding sets is configured to form a current loop with the DC power source Vdc, such that a magnetic field is generated at each of the salient poles B and B′ around which the first and second windings L1 and L2 of said another corresponding one of the phase winding sets are wound, so as to attract the projecting poles b and b′ of the rotor 12 to move toward the salient poles B and B′ of the stator 11. Accordingly, when remaining two of the phase winding sets are sequentially excited in a similar manner, the rotor 12 may be driven to rotate clockwise. Alternatively, if the phase winding sets are sequentially excited in a reverse order, i.e., the phase winding sets wound around the salient poles D and D′, C and C′, B and B′, and A and A′ being excited in sequence, the rotor 12 may be driven to rotate counterclockwise.
However, referring to FIG. 5, when the driving circuit 2 operates in the end of the aforementioned fundamental cycle, so that the first switch Qu and the second switch Qn of the switching member 21 are turned off to be not conducting, instantaneous counter electromotive forces (CEMF) e1 and e2 are induced respectively at the first winding L1 and the second winding L2 of the corresponding one of the phase winding sets. A high current is formed by the CEMFs e1 and e2, and flows via the first flyback diode D1 and the second flyback diode D2 which are coupled electrically between the corresponding one of the phase winding sets and the DC power source Vdc to charge the DC power source Vdc. In this way, the DC power source Vdc, such as a storage battery or a capacitor, is subjected to a high voltage impact, and is thus prone to overheating and burnout due to the instantaneous excessive input current.
Furthermore, structures of projecting poles of the stator 11 and the rotor 12 of the conventional reluctance motor 1 may cause significant cogging torque during a process of phase switching which may result in vibration and noise while the conventional reluctance motor 1 operates.